The invention relates to a seat cover fastening system for seats, and particularly for seats such as are used on trucks and tractors where a covered pad or cushion of resilient material is placed on top of a formed metal seat pan and held thereto by a welt or trim strip which engages both the seat cover and a generally vertical peripheral flange on the seat pan. Examples of prior art seats of this type are shown in British Pat. Nos. 752,215 and 839,143 and in U.S. Pat. No. 3,423,775. In the seats shown in the British patents, a generally J-shaped welt is attached at its top to the seat cover fabric while the bottom is slipped over the lower edge of the seat flange and held in contact therewith by friction. The aforesaid welts can quite easily be removed by pulling them downwardly and thus can be readily vandalized. Furthermore, if the seats on which such welts are used have any substantial amount of padding under the seat cover, the compression of the padding by the seat occupant can tend to force the welt to move downwardly and thus become disengaged from the seat pan flange. U.S. Pat. No. 3,423,775 to Cockerill solves the problem of the seat cover on a cushioned seat becoming unattached during use by wrapping the upholstery material over the flange edge, stepping the flange, and holding the upholstery with a shouldered trim strip which engages the flange steps. In a preferred embodiment, metal clips with barbs are either molded into the trim strip or applied individually to the seat pan. The latter technique is preferred since it serves to anchor the seat cover to the seat pan and correctly position it before the final trim strip is applied. This prior art fastening means is time consuming and relatively costly in that many specially formed clips are used and each one must be manually attached to the seat pan. Furthermore, the seat covers on different seats are not necessarily uniform since the installer can vary the amount of material which is folded over the edge of the flange with the result that successively assembled seats may have covers which are either looser or tighter than desired.